Project Summary/Abstract The pes planus deformity (flatfoot or peritalar subluxation) is the most common foot condition affecting patients of all ages in the U.S. Since the deformity often has a musculotendinous component and many patients have a history of diabetes, hypertension and obesity, the incidence of flatfoot is on the rise. The treatment for peritalar subluxation is not wel-standardized and may involve immobilization, orthotics, and in severe cases, surgical correction. These corective surgeries may include combinations of the folowing: tendon transfers or lengthenings, medial column plantar flexor osteotomies, medial column stabilizations, various hindfoot osteotomies and/or hindfoot arthrodeses. Of note is that there is little agreement among surgeons as to which surgical procedures to perform. The presence of hindfot valgus is a critical piece of information, as symptomatic flatfeet without hindfot valgus can often be corected with a medial column stabilization procedure; however, if hindfoot valgus is present, some measure of calcaneal osteotomy is required. While the specific type of osteotomy is dictated by the pathology of the flatfoot deformity, the most common hindfoot osteotomies (the medializing calcaneal osteotomy (MCO), the Evans calcaneal osteotomy, and the calcaneocuboid distraction arthrodesis (CCDA)) can all lead to increased lateral forefoot pressure. None of these procedures are ideal for pes planus with hindfoot valgus, forefoot abduction and a normal calcaneal pitch angle (a contraindication for lateral column procedures). Additionally, these osteotomies do not offer direct control of correction in all three planes. The calcaneal Z-osteotomy has been demonstrated to allow for correction in all three planes in feet with a varus hindfoot deformity. Recently, the Z-osteotomy has been has been described for corection of the pes planus deformity. The current clinical practice of the orthopaedic surgeon in our group is to perform a modified form of the calcaneal Z-osteotomy to treat pes planus with hindfoot valgus, forefoot abduction and a normal calcaneal pitch angle; however, this procedure has not been objectively studied. The purpose of this study is to compare and contrast the well-established calcaneal osteotomies (MCO and Evans) with the Z-osteotomy by studying bone pose, joint axis and plantar pressure pre- and post- surgery. We will use a highly specialized biplane fluoroscopic system to track the motion of the foot bones of interest. Our Specific Aims [1] To refine our existing biplane fluoroscopic system and [2] To study the fot bone motion of control (neutrally aligned) feet and flatfeet pre- and post-surgery with one of three possible calcaneal osteotomies: the MCO, Evans or Z-calcaneal osteotomy. We have two Philips BV-Pulsera C-arms that are configured to allow a subject to walk through the field of view of both systems while the foot is imaged. We aim to develop new software to track individual bones in high-speed fluoroscopic images, replace the existing CCD cameras with high-speed cameras and mount the X-ray sources and image intensifiers on customized posts that will greatly increase the flexibility of our biplane system. We will quantify the foot bone kinematics and plantar pressures 10 neutrally aligned subjects. We will also quantify the pre- and post-surgical foot bone kinematics and plantar pressures of 30 flat foot subjects, 10 of which will undergo either an MCO, an Evans calcaneal osteotomy or a Z-osteotomy.